1. Field of the Invention
The present invention has to do with dispersible starch products and particularly relates to physically modified starch products prepared using pressure (shear) and heat such as in an extrusion process. The products of the invention have improved functionality in food applications, particularly in instantized hot or cold applications.
2. Description of Related Art
Starches are widely used in food applications as thickeners or bodying agents. They are unique among carbohydrates in occurring as discrete granules. In modern day food processing and storage applications, however, the properties of granular starch must be modified to withstand certain heat, acid and freeze-thaw conditions. Presently, food processors prefer to avoid chemically modified starches and employ natural products such as physically modified starches.
When granular starch is heated in excess water above the gelatinization temperature, it undergoes hydration and gelatinizes, forming a viscous solubilized paste. In practice starch granules require dispersion in cold water before cooking at the time of use.
Pregelatinized starch products have been developed that provide reconstituted pastes when mixed with hot or cold water. The starch manufacturer hydrates the raw starch and then gelatinizes the starch by such techniques as roll-drying or spray-drying and the like. Unfortunately, the dried pregelatinized starch product does not readily disperse in hot water and agglomerated masses are formed giving lumpy pastes with inconsistent paste viscosities.
Attempts have been made to circumvent the dispersibility problem by inclusion of surfactants with dried pregelatinized starch and somewhat improved dispersibilities were obtained as exemplified in U.S. Pat. Nos. 3,537,893; 3,582,350; 3,443,990 an 4,260,642. The effect of surfactants on starch pastes is also described by E. M. Osman in Starch; Chemistry & Technology, Vol. II, Chapter VII, pp. 189-191; Whistler & Paschall Eds., Academic Press, N.Y. (1967).
The term "heat-moisture treated starch" is known in the art and is commonly used to refer to a starch which has been subjected to a heat treatment under controlled moisture conditions, the conditions being such that the starch undergoes neither gelatinization (i.e., exhibits no substantial loss of birefringence) or dextrinization. If heat-moisture treated starches are used in hot-water dispersible foodstuffs, dispersion of the mix into boiling water nevertheless results in formation of lumps and agglomerated or coated masses by surface gelatinization wherein a coating barrier forms on the starch preventing further hydration.
A hot or boiling water dispersible starch product that consistently provides a uniform paste having no lumps or agglomerated masses associated therewith is described in U.S. Pat. No. 4,491,483.
The combination of starch and gums or starch, gums and emulsifiers is generally known (see U.S. Pat. Nos. 3,917,875; 4,140,566; 4,081,567; 4,105,461; 4,119,564; 4,120,986; 4,140,808 and 4,192,900). The gums are used as thickeners or stabilizers in these formulations. Nevertheless, food formulators prefer to use as much starch as possible in these products due to the high cost of gums.
Methods of modifying starch and blends of starch and gums using extrusion are known. U. S. Pat. No. 4,859,484 describes a method of processing starch and gum blends wherein the starch and gum are separately hydrated, intimately commingled and extruded. The method requires water in the amount of 70-200% based on starch weight. Two other U.S. Pat. Nos. 5,208,061 and 5,275,774, describe extrusion methods for making starch products. The use of extrusion to modify starch also has been described by Shaw S. Wang in "Gelatinization and Melting of Starch and Tribochemistry in Extrusion", Starch/Starke 45 (1993) Nr.11, pp 388-390.
Applicants have now discovered an improved method of physically modifying starches and mixtures of starches and other materials using pressure and heat, such as by extrusion under specified conditions of moisture, temperature and pressure. The physically modified products of the improved method can be made for high dispersibility in hot or cold liquids and do not form agglomerated masses.